rs8192678 and rs6949152 Polymorphisms Are Associated with Muscle Fiber Composition in Women.

rs8192678 G/A (Gly482Ser) and rs6949152 A/G polymorphisms have been associated with endurance athlete status, endurance performance phenotypes, and certain health-related markers of different pathologies such as metabolic syndrome, diabetes, and dyslipidemia. We hypothesized that they could be considered interesting candidates for explaining inter-individual variations in muscle fiber composition in humans. We aimed to examine possible associations of these polymorphisms with myosin heavy-chain (MHC) isoforms as markers of muscle fiber compositions in vastus lateralis muscle in a population of 214 healthy Japanese subjects, aged between 19 and 79 years. No significant associations were found in men for any measured variables. In contrast, in women, the rs8192678 A/A genotype was significantly associated with a higher proportion of MHC-I ( = 0.042) and with a lower proportion of MHC-IIx ( = 0.033), and the rs6949152 AA genotype was significantly associated with a higher proportion of MHC-I ( = 0.008) and with a lower proportion of MHC IIx ( = 0.035). In women, the genotype scores of the modes presenting the most significant results for rs8192678 G/A (Gly482Ser) and rs6949152 A/G polymorphisms were significantly associated with MHC-I ( = 0.0007) and MHC IIx ( = 0.0016). That is, women with combined A/A and A/A genotypes presented the highest proportion of MHC-I and the lowest proportion of MHC-IIx, in contrast to women with combined GG+GA and AG+GG genotypes, who presented the lowest proportion of MHC-I and the highest proportion of MHC-IIx. Our results suggest possible associations between these polymorphisms (both individually and in combination) and the inter-individual variability observed in muscle fiber composition in women, but not in men.